Walking would be the best if the elderly can do it. Starting and ending depends on the hotel you are staying at. We were at W so we walked the whole length of the walkway/park leading towards the river. Best time would be to go there just before twilight so you manage to see the beautiful architecture of surrounding buildings both in daylight and night. Opera House and the museum are worth a visit. If you have time you can do a boat ride. Ask the hotel if wheelchairs can be arranged if required.